Carl Icahn is a billionaire financier, ranking #18 on the 2007 Forbes 400 list with an estimated net worth of $14.5 billion.

Icahn built a name for himself in the 1980s as a corporate raider. After keeping quite for years, Icahn made a major comeback as a 'activist investor'. An activist investor agitates companies for changes, including buyouts, share buybacks, and dividend increases.

Icahn has successfully pushed for changes at Time Warner (NYSE: TWX) and Temple-Inland (NYSE: TIN), among others. Icahn won board seats at Motorola (NYSE: MOT) after first failing.

In 2007, Icahn's activism successfully pushed biotech company MedImmune into a sales agreement with AstraZeneca (NYSE: AZN). Icahn is also involved with biotech company Imclone Systems (Nasdaq: IMCL), where he is Chairman of the Board.

In early, 2008 Icahn activist target BEA Systems (Nasdaq: BEAS) was sold to Oracle (Nasdaq: ORCL). Icahn held a 13% stake in BEA.

Icahn is also involved with developments at Biogen Idec (Nasdaq: BIIB) and WCI Communities (NYSE: WCI), which both unsuccessfully explored sales. WCI rejected a $22 per share takeover offer from Icahn in early 2007, only to see its stock plummet on the housing slowdown.

In 2008, Icahn targeted Yahoo! (Nasdaq: YHOO) after the Internet company failed to work out an acceptable merger agreement with Microsoft (Nasdaq: MSFT) Microsoft walked away from its bid for Yahoo! after months of bickering.